1. Field of the Invention
This invention relates to medical devices useful in in vivo environments, in particular, methods and materials used to sterilize such devices prior to their implantation in vivo.
2. Description of Related Art
Medical personnel and patients commonly utilize a wide variety of pre-sterilized medical products, such as glucose sensors that are used by diabetic patients. In this context, a number of different sterilization processes are used with various medical products in order to kill microorganisms that may be present. Most sterilization processes require the sterilizing agent to systemically permeate the article being sterilized. These methods can include heat sterilization, where the object to be sterilized is subjected to heat and pressure, such as in an autoclave. The heat and pressure penetrates though the object being sterilized and after a sufficient time will kill the harmful microorganisms. Gases such as hydrogen peroxide or ethylene oxide are also used to sterilize objects. Sterilization methods also include those that use ionizing radiation, such as gamma-rays, x-rays, or energetic electrons to kill microorganisms.
Radiation has a number of advantages over other sterilization processes including a high penetrating ability, relatively low chemical reactivity, and instantaneous effects without the need to control temperature, pressure, vacuum, or humidity. Consequently, the sterilization of medical devices by exposure to radiation is a common practice. Medical devices composed in whole or in part of polymers are typically sterilized by various kinds of radiation, including, but not limited to, electron beam (e-beam), gamma ray, ultraviolet, infra-red, ion beam, and x-ray sterilization.
Electron-beam and gamma ray sterilization processes provide forms of radiation commonly used to kill microbial organisms on medical devices. However, when used to kill microorganisms, such radiation can alter the structure of functional macromolecules present in medical products including polymers such as proteins. High-energy radiation tends to produce ionization and excitation in polymer molecules, as well as free radicals. These energy-rich species can undergo dissociation, abstraction, chain scission and cross-linking. Electron-beam and gamma ray radiation can therefore be problematical when used to sterilize medical device includes components that are radiation sensitive.
The deterioration of the performance of polymeric materials and other macromolecules in medical devices due to radiation sterilization has been associated with free radical formation during radiation exposure. This complicates the sterilization process and limits the range of designs or materials available for medical devices. In this context, methods and formulations that can protect medical device materials from damage that can occur as a result of exposure to high-energy radiation damage are desirable.